Line scan CRTs are presently important in photorecording applications. Such tubes typically incorporate a narrow plate of glass fiber optics sealed to the output end of the conventional funnel-shaped envelope and in operation a line-at-a-time video-modulated electron beam is deflected or swept across the phosphor-coated inside surface of the fiber optics plate. Modulated light resulting from electrons incident on a phosphor passes through the fiber optics plate and is made incident onto the surface of a photosensitive recording medium that is placed in contact with the outer surface of the fiber optics plate. Line scans are repeated as the medium is moved past the plate in synchronism by means of a stepping motor or continuous drive mechanism attached to a roll or sheet of the medium. Normally, the beam scan is essentially only in the horizontal or (X) direction with the medium moving in the vertical or (Y) direction. Minor modulation of the beam in the (X) direction is usually included to extend the life of the phosphor. As the scans continue and the medium moves, an X-Y image is produced on the photosensitive medium that is subsequently developed and fixed in various ways appropriate to the nature of the medium employed.
The use of a fiber optics plate on the output surface of the CRT simplifies the imaging system since the fiber optics collimates the phosphor light, and makes feasible image formation by direct contact to the medium. This desirably makes for compactness in the recorder, by eliminating the conventional lens-type optical system. However, the length and bulk of the CRT itself still militates against achieving a highly compact assembly. Further, while there have been attempts to substitute solid state devices for the CRT, this proves impractical for recorders designed for wide high quality images, for example images as much as fourteen inches wide.
To avoid this problem, the present invention provides a CRT of novel design that makes for increased compactness.